In the mirror operating mechanism of a conventional single-lens reflex camera, the mirror lifting drive lever and the mirror lowering drive lever are, in general, of the rotary lever type. It is necessary to provide a coil spring because driving the mirror needs a relatively great drive force. The lateral motion range of such a coil spring is large not only because it is stretched but also because the connection point thereof makes a circular motion. Accordingly, heretofore it has been difficult to provide a small mirror operating mechanism suitable for a camera using a small film cassette.